I'm still kind of dumbfounded that the 7 Plus has two cameras side-by-side and apparently ISN'T using them to capture 3D images. One would think this would be the best/most obvious application.
It definitely won't be pretty, but whomever puts the work in will probably benefit from it somehow.
That said how would the phone display the 3D image? One of those cardboard VR things? Not very Appley.
I expect either VR support, 3D imaging, or using them+dynamic light sensing of iPad Pro to have a "reactive" UI where gradients in the UI behave as if they might have real world lighting applied to them
Holding some features back for the next model, perhaps. They have to smooth out the 'wow factor' for each model to keep growth steady.